1. Field of the Invention
The present invention is directed generally to monitoring the operating parameters in a steam turbine generator and, more specifically, to the monitoring of turbine generator shaft torsion.
2. Description of the Prior Art
In many applications it is desirable to measure the torsion experienced by a rotating shaft. That is particularly true when the rotating shaft is employed within a turbine generator. Such shafts are extremely expensive and need to be closely monitored for purposes of scheduling maintenance. It is also desirable to determine what effect a shaft torsional event has had on a turbine generator shaft. Shaft torsional events must be closely monitored to determine whether the shaft is approaching the end of its useful life. Failure to properly predict when a shaft has reached the end of its useful life or when a shaft needs servicing could lead to a catastrophic failure resulting in millions of dollars worth of damage and the loss of life if any personnel happen to be near the turbine generator during such a catastrophic failure.
Conventional torsion monitors employ magnetic sensors that detect the passage of teeth of a toothed wheel located at a selected position on the shaft. The phase shift of a signal produced by the toothed wheel with respect to a once per revolution signal provides an indication that is an accurate measure of the integrated twist of the shaft between the point carrying the toothed wheel and the point generating the once per revolution signal.
To identify various shaft modes, more toothed wheel locations are required. That represents a problem in that the shaft rotates at very high speeds and, because of those high speeds, it is difficult to provide the shaft with the necessary indicia so that signals representative of the shaft's angular position can be produced. Additional problems are encountered because many areas of the shaft are simply not accessible. Thus, the need exists for a turbine generator shaft torsion monitor which can be used in conjunction with conventional turbine generator shafts without requiring substantial modifications.